In the printing of newspapers and similar publications with modern high speed rotary presses it is well known to have the presses and the printing plates used by them so designed that a separate printing plate is used for the printing of each page, or small group of pages, of the newspaper or other publication. This has the advantage that after printing one edition of the publication, a subsequent slightly different later edition can be printed with the pages that remain the same being printed with the same printing plates as in the previous edition and without removing their plates from the press; and with new plates being made and installed on the press only for the changed pages. When the involved publication is one, such as a newspaper, having relatively large size pages the printing plate used for the printing of each page is usually one used only for the printing of that one page. However, in the case of publications having smaller pages each of the separate printing plates used for the printing of the publication may sometimes be used for the printing of two or more of the pages; and the term "printing plate" as used herein includes both those used for printing single pages as well as those used for printing multiple pages.
It is known to produce printing plates by various photolithographic processes wherein the photosensitive surface of a sheet of plate making material is exposed by an imaging system including a laser or other raster scanning plate making machine controlled by scan data representing the image to be printed by the printing plate to be made from the sheet, the scan data modulating the beam, or other scanned element of the machine, as it is scanned in raster fashion across the photosensitive surface of the sheet of plate making material. It is also known to produce printing plates by using an ink jet as the scanned element with the ink jet, for example, being applied as a masking material over the photosensitive surface of a sheet of plate making material and with the photosensitive surface being exposed in a later step.
Some raster scanning plate making machines are of the "flat-bed" type wherein the plate making material is supported on a flat planar support surface during exposure or other processing by the scanned element. Other such machines are of the "external drum" variety wherein the plate making material is supported on the external surface of a rotating drum during processing. Still another type of such plate making machine is the "internal-drum" variety wherein the plate making material is supported on the internal surface of a non-rotating drum during processing. Because of the drum type machines, especially the internal drum type machines, available at the present time being generally of lower cost and/or better accuracy than flat-bed or other types of available plate making machines, there are many instances in which it would be desirable to use a drum type machine for the production of printing plates.
The handling of plate making sheets in the use of drum type machines is, however, fairly intricate and slow. As each sheet of the material is cycled through the machine a significant portion of the cycle time is devoted to the handling of the sheet, such handling for example including pick-up of the sheet from a supply cassette, transfer of the sheet from the supply cassette to the material support surface of the exposure or other raster processing station, placement of the sheet onto the support surface prior to raster processing, pick-up of the sheet from the support surface after raster processing, transport of the sheet from the supporting surface to a receiving cassette, and placement of the sheet into the receiving cassette or transport of the sheet from the support surface directly to the developing machine or station. Further, drum type machines are usually adapted to receive and hold only one sheet of plate making material at a time on the support surface of the raster processing station, and because of the total time required for the processing of each sheet by the machine the number of printing plates produced during any given period of time has been low, and the production rate of such machines may be insufficient to satisfy the demand for printing plates associated with the printing of newspapers and other similar rapidly reissued publications.
The object of this invention is therefore to provide a method of producing page printing plates using an imaging system with a drum type raster scanning plate making machine whereby the number of printing plates produced by the method during a given time period can be significantly increased in comparison to the number of printing plates produced by previous methods.
Other objects and advantages of the invention will be apparent from the following description and drawings describing and illustrating preferred embodiments of the invention and by the appended claims.
Suitable imaging systems for use with the method of this invention include raster scanning machines which are of the internal drum variety using a scanned laser beam and are shown for example by. U.S. patent application Ser. No. 08/071,567 filed Jun. 1, 1993, Pat. No. 5,484,139, entitled "System for Handling Curved Form Media and Cassette Therefore"; by U.S. patent application Ser. No. 08/117,612, Pat. No. 5,619,246, filed Sep. 7, 1993, entitled "Apparatus and Method for Positioning Photosensitive Media on an Exposure Platen"; and by U.S. patent application Ser. No. 08/148,584, Pat. No. 5,558,320, filed Nov. 8, 1993, entitled "Improved Lifting Shoe for Media Handling and Related Cassette Media Holder", all of which applications are owned by the assignee of the present application.